The present invention relates to a particle beam irradiation system, and more particularly to a particle beam irradiation system for use as a particle beam therapy system for exposing a diseased part to a proton, carbon, or other charged particle beam for therapy purposes, a material irradiation system for exposing a material to a charged particle beam, a food irradiation system for exposing food to a charged particle beam, or a radioisotope production system based on a charged particle beam.
A conventional particle beam therapy system comprises a charged particle beam generation apparatus, a beam transport, and a rotary irradiation device. The charged particle beam generation apparatus includes a synchrotron (cyclotron) as an accelerator. After being accelerated to a predefined energy, a charged particle beam (hereinafter referred to as an ion beam) travels to the irradiation device via the beam transport (hereinafter referred to as the first beam transport). The rotary irradiation device includes an irradiation device beam transport (hereinafter referred to as the second beam transport), an irradiation apparatus, and a rotating device (rotary gantry) for rotating the second beam transport and irradiation apparatus as an assembly. The ion beam passes through the second beam transport and then falls on a cancerous part of a patient via the irradiation apparatus.
The irradiation apparatus shapes and emits an ion beam, which is generated by the charged particle beam generation apparatus, in accordance with the shape of a diseased part targeted for irradiation. Roughly speaking, the irradiation apparatus can be divided into three types. The first type is an irradiation apparatus based on a scatterer method. The second type is an irradiation apparatus based on a wobbling method (JP-A No. 211292/1998 and JP-A No. 202047/2000). The third type is an irradiation apparatus based on a scanning method (JP-A No. 199700/1998).
When the interior of a patient's body is to be irradiated with an ion beam emitted from the irradiation apparatus, it is desirable that the radiation dose distribution be uniform in the direction of ion beam propagation (the direction of the depth within the patient's body) and in the direction perpendicular to the direction of ion beam propagation. Such uniformity of radiation dose distribution is especially important within a cancerous area. This uniformity is desired no matter which one of the above-mentioned three types of irradiation apparatuses is used for ion beam irradiation. In a particle beam therapy system containing the aforementioned conventional irradiation apparatus, however, it has been difficult to maintain a high degree of radiation dose distribution uniformity in the direction of the depth while keeping a high radiation dose level particularly for a bulky diseased part (region targeted for irradiation).